This invention relates to methods for texturing substrates used in magnetic disks.
In a conventional disk drive, a recording head "lands" and "takes-off" from a magnetic recording medium surface during the stopping and starting of the drive. When the medium spins at its normal operating rotational velocity, the recording head does not touch the medium, but instead "flies" on an air cushion between the head and the medium. For high recording performance and density, the recording head should be kept as low as possible during flying. This is accomplished by making the medium as smooth as possible. However, if the medium is too smooth, stiction and friction between the head and the medium during starting and stopping of the drive will be excessive. Such excessive friction and stiction adversely affect the overall mechanical reliability of the drive. For example, stiction and friction can cause wear of the recording medium, and eventually a head crash. Thus, recording media manufacturers must provide some roughness on media but not so much as to substantially increase the effective spacing between the magnetic film and the head. It is also noted that roughening the medium may also affect its magnetic properties, and care must be taken to avoid degrading these magnetic properties.
The current approach in industry is to mechanically roughen the medium substrate surface using, for example, a tape embedded with hard particles. When texturing using the tape approach the substrate is usually held on a spindle and rotated at a predetermined velocity while the tape moves over the substrate surface. U.S. Pat. No. 4,973,496, issued Kruger et al., discusses a similar approach, in which an abrasive free tape is fed around a roller and a slurry of abrasive particles is fed onto the tape surface prior to its engagement against the substrate surface.
In a another approach currently used in the industry, a substrate is held by a chuck and rotated over a flat surface having loose hard particles floating in a slurry. This type of machine can be commercially purchased, for example, from Strausbaugh Inc., of California. U.S. Pat. No. 4,698,251, issued to Fukuda et al., teaches such an approach.
In both these approaches, which are practiced by over ninety percent of the media manufacturers, the substrates must be properly cleaned by appropriate apparatus to remove any loose or embedded particles before the substrates are put in sputtering machines for film deposition. Thus, practicing these approaches requires a significant capital investment in the form of both texturing and cleaning apparatus.
It is also known in the art to roughen substrates with chemical etchants. For example, in U.S. Pat. No. 4,326,229, issued to Yanagisawa, radially extending jogs or undulations are formed by spin coating a special solvent onto a substrate surface.
In another approach taught by Tsuya et al. in U.S. Pat. No. 5,047,274, a substrate surface is anodized to form small vertical pores which are then packed by a nonmagnetic material like Cu, and then polished and etched to form a finely roughened surface.
In yet another approach described in U.S. Pat. No. 5,119,258, issued to Tsai et al., the surface of a glass substrate is textured using a plasma etching technique. A similar approach is taught by Doerner et al. in U.S. Pat. No. 5,307,223 for microroughening a NiP plated Al substrate using plasma etching.
As mentioned above, the existing tape texturing or slurry-texturing method requires cleaning and drying steps to remove any loose particle adhering to the substrate surface. This increases the overall manufacturing cost. Similarly, texturing methods requiring chemical etching also require cleaning and drying steps before sputtering. Texturing methods employing plasma etching require a special process station and may suffer from a lack of uniformity of gas flow, thereby reducing yield.
It is also known in the art to zone texture a magnetic medium. In other words, the medium contains a first zone where the read-write head takes off and lands (a "CSS zone"), and a second zone where data is recorded (a "data zone"), wherein the data zone is smooth and the CSS zone is rough. It is also known to provide a "transition region" of gradually decreasing roughness between the CSS and data zones to make it easier for the read-write head to move from the CSS zone to the data zone and back. See, for example, European application EP 0 583 989 A2, incorporated herein by reference. Providing zone texturing with a transition region has been difficult using prior art texturing techniques, and the results have been unsatisfactory.
One object of our invention is to provide a low cost texturing method. Another object of our invention is to provide a high throughput texturing process which can be easily implemented in the apparatus used to deposit the various layers of a magnetic medium. Another object of our invention is to provide a texturing method whereby it is unnecessary to clean the substrate before or after texturing. An object of one embodiment of our invention is to zone texture a magnetic medium and to provide a transition region between the CSS and data zones.